1. Field of the Invention
This invention relates to a rear view periscopic device and an optical train therefor.
2. Prior Art
Heretofore, numerous efforts have been made to provide a rear viewing optical device for vehicular use which enables the user to see a true perspective view of objects behind an observer. Many of the earlier devices employed a rearward directed objective lens mounted in the upper portion of a tube member extending well above a vehicle roof and arranged to direct an image downward for viewing by the vehicle driver on a display surface. The primary problem with these designs has been their small visual fields and their bulky size. In constructing these periscopic devices, the required spacing between the objective lens and the image receiving surface plus the placement of image directing and image corrective mirrors produced an unacceptable proportioned device, even though many advantages made their use highly desirable. Most of these past designs required that a considerable portion of the device extended well above the vehicle roof line in which it was used to the detriment of the vehicle's appearance and which created an obstacle subject to damage. Further, a considerable portion of the device extended downward into the vehicle producing a safety hazard as well as obscuring the forward view.
More recently, certain periscopic devices have been devised to provide an extremely wide field of view for an over-the-top system of rear viewing which utilizes a pair of very wide mirrors mounted in the roof of a vehicle to bring an image to the driver's viewing mirror. Herein, the advantage of providing a wide angle rear view display system is overshadowed by the numerous objectional features, primarily due to the device's size. Namely, headroom obstruction; necessity for a wide roof opening, resulting in a weakened roof; high cost; subject to vibration; high wind resistance; defrosting and cleaning difficulties; limitations in viewing mirror location; and aesthetic considerations.